Determination and correlation of solubility and Thermodynamic properties of allantoin in four binary solvents from 288.15 K to 333.15 K

The solid–liquid equilibrium data of allantoin were determined by gravimetric method in four binary solvents (methanol-water, ethanol-water, ethylene glycol-water and methanol-ethylene glycol) at temperatures ranging from 288.15 to 333.15 K. The allantoin exhibited high solubility in ethylene glycol-water solvents. The solubility increased and then decreased with the increasing ratio of ethanol to water above 318.15 K. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) indicated that allantoin would be decomposed above 505 K (T5%). X-ray diffraction (XRD) showed that no crystalline transformation occurred in the investigated system. In the meanwhile, the experimental data were correlated by four thermodynamic models including modified Apelblat equation, Van't Hoff equation, Jouyban–Acree model, and λh equation. All the models fitted well with the experimental data. This study can help the industrial crystallization of allantoin.